This invention relates generally to automatic electric cigar lighter devices intended for use in automobiles and the like, and more particularly to lighters of this type which are especially adapted to heat to useful incandescence in relatively short intervals of time.
In the past, a large volume of automatic electric cigar lighter constructions for automobiles has been proposed and produced. Generally, such lighters employed a set of bimetallic spring fingers disposed in the socket of a holder device, which were engageable with side surfaces of a heating element cup carried at the inner end of the ignitor plug. When the plug was depressed, the fingers latched over the sides of the heating element cup, establishing a circuit through the element. As the element reached useful incandescence, the bimetallic fingers became heated and would then spread and release the cup and the ignitor plug, enabling these to retract and break the circuit through the element.
Numerous refinements of this basic structure were achieved over the years. Even so, problems sometimes arose, as when one of the bimetallic fingers, for reasons often obscure, shifted into the path of the ignitor plug while the latter was being depressed, resulting in breakage and possible short-circuiting of the socket. This would cause either a blown fuse or else a burned-out wiring harness, depending on the type of current overload protection built into the particular electrical system of the automobile. In other cases, the bimetallic fingers underwent an aging deformation after prolonged use. When this occurred, the socket usually had to be removed, in most cases involving work underneath or to the rear of the dashboard. Where the socket was not readily accessible, such repair or replacement became difficult, costly and time consuming.
Typically, in automatic lighters, there is a period of from ten to fifteen seconds following the actuation of the ignitor plug, until the heating element has reached useful incandescence that is sufficient to enable the plug to snap out in readiness for use. In the past, a number of efforts have been made to reduce this waiting time to just a few seconds. Several such innovative units have employed a bimetal disk disposed adjacent to the heating element, the disk itself constituting one contact of the switch which was adapted to open after the element reached incandescence. By positioning the disk right next to the element, response times on the order of only several seconds were achieved, particularly when an applied voltage was used which exceeded the continuous voltage rating of the heating element.
Various prior lighters of the type employing bimetallic disks had distinct disadvantages. Generally where the contact area of the disk was at its center, the socket was arranged to permanently fasten or mount the disk at its periphery. This mounting for the disk had to be such that it would not interfere with the flexing and snap-type movements thereof, thereby imposing stringent requirements on the tolerances of both the disk and the part or parts which carried it. Also, in most cases, the disk constituted part of the current-carrying circuit, and thus had to be insulated from the remaining parts of the socket. Accordingly, such mountings were often awkward and prone to malfunction in use.
In other constructions, as where the contact area of the disk was at its periphery, the disk was mounted by means of a stud passing through a hole in its center, the end of the stud being staked to hold the disk in place. The problem with this arrangement was that the support area was too small, and the disk eventually loosened, causing poor electrical contact with the stud. Or, if the support area was made sufficiently large, then its freedom of movement was impaired, as well as its proper functioning. Since both the stud and the disk were current-carrying members, any loosening caused either an excessive voltage drop, or else an open circuit, resulting in malfunction or failure of the device. Where the bimetallic disk itself was employed as one contact of the circuit-breaking switch, there occurred burning and pitting at the points of contact, this resulting in both a poor electrical connection and in deterioration of the disk itself, after a period of use. Moreover, where the disk was a current carrier, the relatively heavy current flow associated with ignitor devices resulted in resistance-heating of the disk, aside from the heating effect due to its proximity to the coil. The resistance or self-heating effect depended on the resistances of the electrical path through the disk and stud; there were thus introduced other undesirable variables into the design of the ligher, which caused problems during manufacturing runs where large numbers of units were to be mass produced, from components possibly having slightly different physical and/or electrical characteristics. In addition, in constructions where the bimetallic member was arranged to carry the heating element current, the response time of the member was very adversely affected by energy changes which occurred in the vehicle electrical system, such as drops in the supply voltage resulting from the application of momentary loads by other equipment in the vehicle, or surges in the supply voltage resulting from variation in the rate of charging by the vehicle's alternator or generator. Such variations in the applied voltage resulted in significant corresponding changes in the self-heating effect of the current on the bimetallic member, tending to exaggerate existing non-uniformities of response over prolonged periods of operation and under different environmental conditions.
Applicants' copending application, U.S. Ser. No. 868,935 identified above, discloses an arrangement for a fast-acting manual cigar lighter wherein the manually operable part of the ignitor plug is depressed and held for several seconds, to thereby close the heating element circuit and cause the element to reach incandescence, after which the circuit is automatically opened by a disk-like bimetallic member which is carried in the plug itself.
This particular construction has been found to operate quite well from the standpoint of good reliability and long life expectancy. The number of individual parts required in this prior design has led to attempts to simplify the construction somewhat, so as to reduce the overall manufacturing cost and result in easier assembly. Cigar lighters of the above type are typically built in manufacturing runs of thousands of units. Some of the newer luxury automobiles are provided with four or more of such lighter devices; it can be readily appreciated that the annual sales of such units can easily run into the hundreds of thousands. Accordingly any saving which can be realized, as by reducing the number of parts involved, reducing the cost of such parts, and simplifying the assembly, becomes especially important from an economic standpoint. Of course, while it is considered desirable to reduce the costs of such items as much as possible, it should be realized that these devices must perform in a satisfactory manner, with complete freedom from jamming or malfunctioning, over the projected life of the automobile, which can be a number of years. Conceivably such devices can be subjected to thousands of operations over the life of the car, and in fact, production samples are tested for performance in excess of such figures.
In another of applicants' copending applications identified above, a fast-acting manual cigar lighter has a normally-closed electrical switch controlled by a non-current carrying disk, the disk being carried in the holder device instead of by the plug. This resulted in fewer and simpler parts, with resulting economies while still providing for excellent performance and reliability.